With nearly 60 inches of rainfall annually, Juneau, Alaska, is one of the wettest cities in the United States. As you can imagine, that makes building and maintaining trails a challenge. But Juneau Mountain Bike Alliance (JMBA) has found a workaround, using crushed shale, a natural product of river runoff. They’ve used crushed shale at the nearby Thunder Mountain Bike Park, which they recently completed, and they’re also transporting it to trails in surrounding areas.
JMBA has nearly completed Thunder Mountain Bike Park
Thunder Mountain Bike Park, in the Under Thunder Trail Network in Mendenhall Valley, just northwest of Juneau, is the first purpose-built bike park in the region. The park currently has seven trails, six of them directional and downhill-only.
Reid Harris, former JMBA President and founding member, told us that the bike park is all but wrapped up. As it stands, Thunder Mountain consists of two green trails, two blues, and three black trails. Of all the trails at the park, “Thunder Mountain Uptrack” is the only multi-directional trail. While riders can descend this green trail, it also serves as the most direct climb from the Under Thunder trailhead.
Right next door is “Dream Zone,” the descending-only green option at Thunder Mountain. Harris said that the park overall is built around progression. Green trail rollers turn into tabletops on the blue trails and eventually doubles on the black trails. Along with doubles on the black trails, JMBA has also utilized a good number of wooden features.
Harris said a lot of attention has been given to a trail called “Bob Gnarly” thanks to a feature that might go a bit beyond its advanced rating. “That’s the big jump line,” he explained. “It’s a black-created line, but there’s definitely a double-black feature on there, which is this big step up onto a bridge. I think it’s an eight-foot air gap, and it steps up about two feet.”
JMBA just completed “Spruce Dust” this year, complementing “In the Gnome of Love,” which had been around for a handful of years. Both are intermediate trails, and both are good progression feeders into the bigger jump lines like Bob Gnarly and another advanced jump line, “BTV.”
Those looking for a bit more of a traditional singletrack experience will likely enjoy “Paydirt.” The trail is the oldest at Thunder Mountain and is roughly twice as long, stretching to roughly half a mile. It also drops more elevation. While nearly all the other trails at the bike park have around 100 feet of elevation loss, Paydirt drops 150 feet.
The secret sauce at Thunder Mountain is crushed shale
Rain or shine (in Juneau, it is mostly rain), residents and visitors alike are sending lap after lap down the different trails. Harris and JMBA point to one interesting natural resource as a main reason for the trails’ success — crushed shale.
“With the bike park, there’s this unique soil out there, this crushed shale,” Harris said. “If you look at it really closely, it’s like platelets, like little flat disks of rock.”
JMBA lucked out for a few reasons with this crushed shale. First, it is easily accessible. The crushed shale is found in the rivers and land that surround Thunder Mountain, so getting it to the trails is relatively easy. Second, Harris told us the crushed shale compacts well and sheds water effectively. With over 250 days of precipitation each year, Juneau is certainly a place where the trails need to shed water.
Along with compacting and shedding water well, the crushed shale also requires little maintenance. “One of the first of those trails [to be built with the crushed shale] was built five years ago, and we’ve done hardly anything to it.”
But the most important aspect of using the crushed shale is how it is helping the local salmon population. Harris told us the shale is a natural deposit coming from the nearby mountains. It enters the streams and gets deposited lower down, where it flattens out.
“The city has a couple of catchment systems to keep all that [crushed shale] from blocking up the salmon stream downriver,” Harris explained. “They started putting these giant piles of it all over the place.”
And JMBA was happy to use the crushed shale. The city will remove more each year, and JMBA will keep adding it to trails where needed. Harris said they have even started transporting the crushed shale to trail systems a bit further away from Thunder Mountain Bike Park. While it is a bit slower and more costly, the shale essentially armors the trails, making the extra work worth it.
Thunder Mountain is for the young senders
Juneau had a lot of trails that are multiuse, which are fun to ride on, but mountain biking has developed in this community, Harris told us. “There has been a demand for more bike-specific trails, and Thunder Mountain is the absolute pinnacle of that.”
Harris explained that the Juneau area has a good population of younger riders who like to “push big dual-crown bikes” up the hill seeking gnarly trails. Now, those riders and others have a place that provides a more gravity-oriented experience.
He also mentioned intentionality behind the location of the bike park. While it was important to be close to the crushed shale deposits, JMBA also recognized that Mendenhall Valley would benefit from the trails.
“The valley, which is where 75% of the population lives, didn’t have a lot in terms of actual mountain bike-specific trails,” Harris said. “It also has a lot of families with young kids.”
And JMBA isn’t done at Thunder Mountain. Harris told us that they have one more trail planned — an adaptive trail between Dream Zone and In the Gnome of Love. While JMBA couldn’t share much about the new trail because they are still in the early planning stages, one thing is for sure: they will incorporate crushed shale in the build.
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